Over the past several years a growing family of leukocyte chemoattractant/activating factors, termed chemokines, has been described (Oppenheim, J. J. et al., Annu. Rev. Immunol., 9:617-648 (1991); Schall and Bacon, Curr. Opin. Immunol., 6:865-873 (1994); Baggiolini, M., et al., Adv. Immunol., 55:97-179 (1994)). Members of this family are produced and secreted by many cell types in response to early inflammatory mediators such as IL-1β or TNFα. The chemokine superfamily comprises two main branches: the α-chemokines (or CXC chemokines) and the β-chemokines (CC chemokines). The α-chemokine branch includes proteins such as IL-8, neutrophil activating peptide-2 (NAP-2), melanoma growth stimulatory activity (MGSA/gro or GROα), and ENA-78, each of which have attracting and activating effects predominantly on neutrophils. The members of the β-chemokine branch affect other cell types such as monocytes, lymphocytes, basophils, and eosinophils (Oppenheim, J. J. et al., Annu. Rev. Immunol., 9:617-648 (1991); Baggiolini, M., et al., Adv. Immunol., 55:97-179 (1994); Miller and Krangel, Crit. Rev. Immunol., 12:17-46 (1992); Jose, P. J., et al., J. Exp. Med., 179:881-118 (1994); Ponath, P. D., et al., J. Clin. Invest., 97:604-612 (1996)), and include proteins such as monocyte chemotactic proteins 1-4 (MCP-1, MCP-2, MCP-3, and MCP-4), RANTES, and macrophage inflammatory proteins (MIP-1α, MIP-1β). Recently a new class of membrane-bound chemokines designated CX3C chemokines has been identified (Bazan, J. F., et al., Nature 385:640-644 (1997)). Chemokines can mediate a range of pro-inflammatory effects on leukocytes, such as triggering of chemotaxis, degranulation, synthesis of lipid mediators, and integrin activation (Oppenheim, J. J. et al., Annu. Rev. Immunol., 9:617-648 (1991); Baggiolini, M., et al., Adv. Immunol., 55:97-179 (1994); Miller, M. D. and Krangel, M. S., Crit. Rev. Immunol., 12:17-46 (1992)). Lately, certain β-chemokines have been shown to suppress HIV-1 infection of human T cell lines in vitro (Cocchi, F., et al., Science (Washington D.C.), 270:1811-1815 (1995)).
Chemokines bind to 7 transmembrane spanning (7TMS) G protein-coupled receptors (Murphy, P. M., Annu. Rev. Immunol., 12:593-633 (1994)). Some known receptors for the CC or β chemokines include CCR1, which binds MIP-1α and RANTES (Neote, K., et al., Cell, 72:415-425 (1993); Gao, J. L., J. Exp. Med., 177:1421-1427 (1993)); CCR2, which binds chemokines including MCP-1, MCP-2, MCP-3 and MCP-4 (Charo, I. F., et al., Proc. Natl. Acad. Sci. USA, 91:2752-2756 (1994); Myers, S. J., et al., J. Biol. Chem., 270:5786-5792 (1995); Gong et al., J. Biol Chem 272:11682-11685 (1997); Garcia-Zepeda et al., J. Immunol. 157:5613-5626 (1996)); CCR3, which binds chemokines including eotaxin, RANTES and MCP-3 (Ponath, P. D., et al., J. Exp. Med., 183:2437-2448 (1996)); CCR4, which has been found to signal in response to MCP-1, MIP-1α, and RANTES (Power, C. A., et al., J. Biol. Chem., 270:19495-19500 (1995)); and CCR5, which has been shown to signal in response to MIP-1α, MIP-1β and RANTES (Boring, L., et al., J. Biol. Chem., 271 (13):7551-7558 (1996); Raport, C. J., J. Biol. Chem., 271:17161-17166 (1996); and Samson, M. et al., Biochemistry, 35:3362-3367 (1996)).
CCR2 is expressed on the surface of several leukocyte subsets, and appears to be expressed in two slightly different forms (CCR2a and CCR2b) due to alternative splicing of the mRNA encoding the carboxy-terminal region (Charo et al., Proc. Natl. Acad. Sci. USA 91:2752-2756 (1994)). MCP-1 acts upon monocytes, lymphocytes and basophils, inducing chemotaxis, granule release, respiratory burst and histamine and cytokine release. Studies have suggested that MCP-1 is implicated in the pathology of diseases such as rheumatoid arthritis, atherosclerosis, granulomatous diseases and multiple sclerosis (Koch, J. Clin. Invest. 90:772-79 (1992); Hosaka et al., Clin. Exp. Immunol. 97:451-457 (1994); Schwartz et al., Am. J. Cardiol. 71(6):9B-14B (1993); Schimmer et al., J. Immunol. 160:1466-1471 (1998); Flory et al., Lab. Invest. 69:396-404 (1993); Gong et al., J. Exp. Med. 186:131-137 (1997)). Additionally, CCR2 can act as a co-receptor for HIV (Connor et al., J. Exp. Med. 185:621-628 (1997)). Thus, CCR2 receptor antagonists may represent a new class of important therapeutic agents.